Flame-retardant, impact-resistant modified polycarbonate molding compositions are known. Compounds which contain phosphorus, particularly aromatic esters of phosphoric acid, are often used as flame retardants on a large industrial scale.
U.S. Pat. No. 5,061,745 describes polymer mixtures comprising aromatic polycarbonates, ABS graft polymers and/or styrene-containing copolymers and esters of monophosphoric acid as flame retardant additives. One disadvantage of esters of monophosphoric acid is their plasticizing effect, which results in a considerable decrease in the dimensional stability of these polymers under the effect of heat. Moreover, for many applications these compounds are too volatile and exhibit too great a capacity for migration in the polymer composition, which under unfavorable injection molding conditions may result in the bleeding out of the flame-retardant additive and in unwanted contamination of the surfaces of the injection mold, which is termed a “juicing phenomenon”.
Said juicing phenomenon may be very substantially suppressed, and the dimensional stability under the effect of heat of the material may easily be increased, by the use of oligomers of esters of phosphoric acid or mixtures of oligo- and monophosphoric acid esters as flame retardants in PC/ABS-molding compositions, as described in EP-A 0 363 608 and EP-A 0 640 655. For many applications, however, the dimensional stability under the effect of heat which is thereby obtained is still unsatisfactory.
WO 99/07779 describes the use of oligophosphates based on bi-phenylene dihydroxide as flame retardants in PC/ABS molding compositions. These phosphates exert a significantly reduced plasticiser effect on the polymer composition, so that a greater dimensional stability under the effect of heat may be achieved. However, molding compositions which are provided with this additive exhibit poor flowability, which in many cases is not satisfactory for the processing of the material by injection molding.
Other esters of oligophosphoric acid and the use thereof as flame retardants in PC/ABS molding compositions are described in EP-A 0 816 434 (oligophosphates based on bisphenol S), EP-A 0 672 717 (alkyl-substituted oligophosphates of the p-hydroquinone type), U.S. Pat. No. 5,455,292 (alkyl-substituted oligophosphates based on bisphenol A), U.S. Pat. No. 5,864,004 (oligophosphates based on bisphenol A) and U.S. Pat. No. 5,183,905 (oligophosphates based on phenolphthalein). PC/ABS molding compositions which are made flame-retardant with these compounds do in fact exhibit dimensional stability under the effect of heat which is improved compared with that achieved with conventional flame retardants, but for many applications still do not exhibit sufficient dimensional stability under the effect of heat or exhibit deficiencies in flowability or toughness.